A vector network analyzer (VNA) is a reflectometer-based electronic instrument that can be used to measure the frequency response (magnitude and phase) of a device under test (DUT) such as an electrical network, component, circuit, or sub-assembly. A VNA makes use of a frequency sweeping source or stimulus, directional couplers, and one or more receivers that provide ratioed amplitude and phase information such as reflection and transmission coefficients.
Referring to FIG. 1, a VNA 100 is shown connected to a DUT 2. The VNA 100 makes use of a reflectometer receiver 102 for signal separation and detection. The directional couplers divert signal power from a main line 101 to which they are coupled. These couplers separate the waves that are incident on and reflected from the DUT 2. The reflectometer receiver 102 uses a local oscillator (LO) 108 (also referred to herein as a strobe source) to mix an RF signal or stimulus from the RF source (also referred to herein as an input) 106 down to a lower intermediate frequency (IF) signal. A frequency reference 104 acts as a stable oscillator that can be used for frequency calibration or reference. The LO 108 is either phase-locked to the RF or the IF signal so that the reflectometer receiver 102 is tuned to the RF signal present at the RF source 106. The incident wave and related signal paths are indicated by an “a” and the reflected wave and related signal paths are indicated by a “b”. The IF signals (IFa, IFb) can be provided to a processor 112 for signal conditioning and provided to a data display 114 for displaying the amplitude and phase information obtained from the IF signals. VNAs have limited bandwidth often designed for intended use (e.g., general class of DUTs targeted), and/or unit cost. It is therefore useful to supplement a VNA with a mechanism that can extend the bandwidth of the VNA.